How can I adjust my code so that the value that I print with my BLE device does not get chopped up when I receive it on an app?

Question

I am using a BLE device (https://www.adafruit.com/product/1697) that I use to print data to an app. I can successfully connect the BLE to the app and receive the data but the result however gets chopped up.

What I am sending is a lat, lng value (that I gather with a library called TinyGPS++ http://arduiniana.org/libraries/tinygpsplus/) and the code looks like this:

BTLEserial.Print::print(gps.location.lat(), 8);
BTLEserial.print (", ");
BTLEserial.Print::print(gps.location.lng(), 8);

So for example if the latitude is: 32.12345678, it comes like this to the app: 3, new row, 2, new row etc.

So my question is, how can I adjust my code to make sure it does not send the result chopped up but instead sends it's complete value?

• Chris Stratton: Your app code is invalidly assuming the data will arrive in a single receive API call. You can only fix the issue by fixing the app. Timing related things you do on the arduino mightvstatistically influence the outcome, but the only sound solution is fundamentally correct receiving code.
• Martman: The answer below fixed my issue though by sending it as string
• Chris Stratton: No, not really. It may unreliably appear to work more often but it is wrong and based on fundamental misunderstanding. Between your ardunio and your app you have a serial link and a packetized one neither of which respects your original grouping in a more than happenstance way.
• Martman: As far as i can see it sends data my app and i receive it nicely just the way i want it (not chopped). I have tested it like 30 seconds though (as it keeps sending data each 2 seconds) and maybe i could face issues with a longer connection you mean? Or will there be a issue with lat, lng accuracay (value not updating)?
• Chris Stratton: Or you could face an issue when the computational load on your phone or the phase of the moon or the local RF environment changes. That is the cost of invalid assumptions in software. The only valid solution is to find the end of a message by an explicit condition.

Answer 1

how can I adjust my code to make sure it does not send the result chopped up but instead sends it's complete value?

The BLE device uses a package approach and the print member functions only support strings (char vectors and Arduino String). Construct the message as a String:

double lat = gps.location.lat();
double lng = gps.location.lng();
String msg = String(lat, 8) + String(", ") + String(lng, 8);
BTLEserial.print(msg); 

Cheers!

• Martman: The first lat value works! But with the lng value a new row is created after 4 decimals has been made, so it look like this when I get it on the app now: 36.02331400, 19.7794(new row)4300
• Martman: So 4300 in this case gets on a new row
• Martman: Ah, is it because 20 bytes is max to send?
• Martman: With "." and "," and "space" the totalt amount of byte is 24
• Mikael Patel: Or fix your app so that it reconstructs a line of text, i.e. reads messages until new-line/carriage-return.